The present invention relates to dithienobenzothiophenes, to a process for their preparation and to their use as semiconductors or charge transport materials.
The formidable building block for the development of (micro)electronics during the last one-half of the 20th century is the field-effect transistor (FET) based on inorganic electrodes, insulators, and semiconductors. These materials have proven to be reliable, highly efficient, and with performance that increases periodically according to the well-known Moore's law. Rather than competing with conventional silicon technologies, an organic FET (OFET) based on molecular and polymeric materials may find large scale applications in low-performance memory elements as well as integrated optoelectronic devices, such as pixel drive and switching elements in active-matrix organic light-emitting diode displays, RFID tags, smart-ID tags, and sensors.
The use of organic semiconductors in OTFTs has some advantages over the inorganic semiconductors used to date. They can be processed in any form, from the fiber to the film, exhibit a high mechanical flexibility, can be produced at low cost and have a low weight. The significant advantage is, however, the possibility of producing the entire semiconductor component by deposition of the layers from solution on a polymer substrate at atmospheric pressure, for example by printing techniques, such that inexpensively producible FETs are obtained.
Among the organic semiconductors used in OFETs, oligothiophenes, polythiophenes, acenes, rylenes, and phthalocyanenes are the most investigated. For instance, the first report on a polyheterocycle-based FET was on polythiophene. In addition, poly(3-hexyl)thiophene and α,ω-dialkyloligothiophenes were the first high-mobility polymer and small molecules, respectively. Over the years, chemical modifications of these compounds, including variations in ring-to-ring connectivity and substitution pattern, have resulted in a considerable number of electro-active materials.
The performance of the electronic devices depends essentially on the mobility of the charge carriers in the semiconductor material and the ratio between the current in the on-state and the off-state (on/off ratio). An ideal semiconductor therefore has a minimum conductivity in the switched-off state and a maximum charge carrier mobility in the switched-on state (mobility above 10−3 cm2V−1s−1 on/off ratio above 102). In addition, the semiconductor material has to be relatively stable to oxidation, i.e. has to have a sufficiently high ionization potential, since its oxidative degradation reduces the performance of the component.
One of the most widely used organic p-type semiconductors is pentacene which typically shows mobilities greater than 1.5 cm2/Vs. Due to its polymorphic structure and its need to be deposited from the vapour phase, this acene derivative complicates device studies (Lin et al. IEEE Trans. Electron Devices 1997, 44, 1325). Solution processable derivatives of pentacene have been reported, exhibiting charge carrier mobilities of 1.8 cm2/Vs (Park et al. 2005 Int. Electron. Dev. Mtg. Technol. Digest 2006, 113). Nevertheless the general instability of the higher acenes hampers the wide utilization in final applications.
WO 2008/026602 discloses unsubstituted and substituted [1]benzothieno[3,2-b][1]benzothiophene as organic semiconductors. These compounds are substituted in 3,8 position, and, respectively, in 2,7 position, with n-C6H13, n-C6F13, phenyl, pentafluorophenyl, p-trifluoromethylphenyl and diphenylyl. Disclosed is also unsubstituted Naphtho[2,3-b]naphtho[2′3′:4,5]thieno[2,3-d]thienophene.
JP 2008-10541 A discloses substituted benzo[1″,2″:4,5; 4″,5″:4′,5]dithieno[3,2-b:3′,2′-b′]bis[1]benzothiophene which is substituted in 6,13-position with tris(1-methyl-ethyl)silylethinyl and with 4-hexyl-2,6-diisopropylphenyl respectively. FETs utilising components of this structure class are reported to reach a maximum mobility of 0.47 cm2/Vs.
For the reported, high performance small molecule semiconductors the reaction routes are lengthy and often low yielding.